Most yo-yos typically comprise two disk-shaped side portions that are rigidly connected to each other by some form of axle structure. The side portions are usually of unitary construction and may be made out of plastic, metal or wood. The axle structure is normally secured to the center of both side portions and can be an assembly having multiple parts, or merely be in the form of a dowel or a riveted pin. In many modern yo-yos, a ball bearing unit, or other rotatable member, is secured to, and has at least a portion rotatable on, a center portion of the axle structure.
The axle structure also forms an anchor for one end of a string-type tether. An end-located loop portion of the tether is positioned so that it encircles a center portion of the axle structure. The free end of the tether is usually tied to create a second loop portion that can be placed about one of a user's fingers to thereby secure the yo-yo to the user's hand.
When one end of the tether is secured to a user's finger and the remainder of the tether is wound about the axle structure, the yo-yo is ready for use. When the yo-yo is released, or thrown, from the user's hand, the yo-yo will begin to rapidly spin as the tether unwinds from about the axle structure and the yo-yo moves away from the user's hand. Once the tether is fully unwound, the yo-yo may “sleep” at the end of the tether, whereby the yo-yo's side portions continue to spin without the tether rewinding on the axle structure. This is enabled by either having the tether's end loop slip on the axle structure, or by having the tether's end loop secured to a freely rotatable member that is secured to, or forms a portion of, the axle structure. Once the yo-yo is sleeping, there are a number of tricks, such as “walk the dog,” that a user can perform with the spinning yo-yo.
When a typical yo-yo is sleeping at the end of the tether and the user wishes to cause the yo-yo to return to his or her hand, the user will make a quick tug/jerk on the yo-yo's tether. This results in a brief tightening of the tether, and is automatically followed by a temporary slackening of the tether. Once the tether goes slack, the tether proximate the axle structure can engage and become movable with the spinning portion of the yo-yo. Continued rotation of the spinning portion of the yo-yo will then cause the tether to wind about the axle structure, resulting in the yo-yo's return to the user's hand.
An extremely important performance characteristic of a yo-yo is its potential sleep time. Since most yo-yo tricks are performed while the yo-yo is sleeping, the longer a yo-yo can be made to sleep, the more time a user will have to complete any particular yo-yo trick. While some tricks can be performed quickly, others require a yo-yo that is capable of sleeping for a relatively long period of time.
In our U.S. Pat. No. 7,448,934 (hereby incorporated by reference), we taught a yo-yo that includes at least one powered rotation system. Said system enables a yo-yo to sleep for significantly longer than other prior art yo-yos and enables a user to perform yo-yo tricks practically without sleep time limitations. However, since said yo-yo is electrically powered, it would be advantageous to increase its efficiency to thereby either increase the time it can sleep or to be able to have the same sleep time while using less energy.